Re: How to know/decide if it is wrong English or slang or colloquial?
For info, in BrE, it would be correct to say either "It smells really bad" or "It stinks really badly" but not a combination of the two. The same might not be true for AmE.
However, in the example you gave, the report was repeating exactly what the person actually said. When quoting people's words, it should be done so verbatim, regardless of whether the writer of the report believes that what the person said was grammatical or not.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.